1. Field of the Invention
The invention relates to slide fasteners and to methods and apparatus for manufacturing slide fasteners. The invention particularly relates to slide fasteners employing trains of fastener elements molded on parallel filaments.
2. Description of the Prior Art
The prior art, as exemplified in U.S. Pat. Nos. 2,496,926, 3,328,857, 3,444,948, 3,445,915, 3,487,531 and 3,770,862 and Great Britain Patent 446,336 contains many types of slide fasteners including fasteners with trains of fastener elements molded on parallel filaments as well as methods and apparatus for manufacturing the same. Pairs of leg portions of the fastener elements extending in opposite directions from head portions are folded together to form base portions which are sewn or woven to the edge of a carrier tape.
Previous fastener elements in trains molded on parallel filaments had leg portions with flat facing surfaces; such flat facing surfaces allowing relative lateral movement therebetween which can result in distortion of the fastener elements and degradation of their fastening ability.
In forming stringers wherein the filaments of the trains of fastener elements are used to at least partially support or hold the fastener elements on the edge of the carrier tapes, the filaments are often torn from the fastener elements due to the shallow depth to which the filaments are embedded in the fastening element; for the same reason, the fastener elements of such prior art stringers can not withstand large lateral forces, the fastener elements being readily pulled from the filaments and stringers.
In prior art apparatus for producing molded trains of fastener elements, the friction between plastic injection shoes and cavity wheels results in wear of the cavity wheels requiring them to be periodically replaced.
Head portions of molded fastener element trains must have tapered projections with underside surfaces sloping upward to allow proper interlocking and release between opposing fastener element trains. Due to the resulting flat underside surfaces on the head portions formed by the sliding of prior art injection shoes over the cavities or by linear shaving, it was previously necessary to form the upward-sloping underside surfaces on the head projections during the folding of the leg portions; such forming requiring additional steps or particular control of the fastener elements.